Lib/site.py

"""Append module search paths for third-party packages to sys.path.

****************************************************************
* This module is automatically imported during initialization. *
****************************************************************

This will append site-specific paths to the module search path.  On
Unix (including Mac OSX), it starts with sys.prefix and
sys.exec_prefix (if different) and appends
lib/python<version>/site-packages.
On other platforms (such as Windows), it tries each of the
prefixes directly, as well as with lib/site-packages appended.  The
resulting directories, if they exist, are appended to sys.path, and
also inspected for path configuration files.

If a file named "pyvenv.cfg" exists one directory above sys.executable,
sys.prefix and sys.exec_prefix are set to that directory and
it is also checked for site-packages (sys.base_prefix and
sys.base_exec_prefix will always be the "real" prefixes of the Python
installation). If "pyvenv.cfg" (a bootstrap configuration file) contains
the key "include-system-site-packages" set to "true" (case-insensitive),
the system-level prefixes will still also be searched for site-packages;
otherwise they won't.

Two kinds of configuration files are processed in each site-packages
directory:

- <name>.pth files extend sys.path with additional directories (one per
  line).  Lines starting with "import" are deprecated (see PEP 829).

- <name>.start files specify startup entry points using the pkg.mod:callable
  syntax.  These are resolved via pkgutil.resolve_name() and called with no
  arguments.

When called from main(), all .pth path extensions are applied before any
.start entry points are executed, ensuring that paths are available before
startup code runs.

See the documentation for the site module for full details:
https://docs.python.org/3/library/site.html
"""

import sys
import os
import builtins
import _sitebuiltins
import _io as io
import stat
import errno

lazy import locale
lazy import pkgutil
lazy import traceback
lazy import warnings

# Prefixes for site-packages; add additional prefixes like /usr/local here
PREFIXES = [sys.prefix, sys.exec_prefix]
# Enable per user site-packages directory
# set it to False to disable the feature or True to force the feature
ENABLE_USER_SITE = None

# for distutils.commands.install
# These values are initialized by the getuserbase() and getusersitepackages()
# functions, through the main() function when Python starts.
USER_SITE = None
USER_BASE = None


def _trace(message, exc=None):
    if sys.flags.verbose:
        _print_error(message, exc)


def _print_error(message, exc=None):
    """Print an error message to stderr, optionally with a formatted traceback."""
    print(message, file=sys.stderr)
    if exc is not None:
        for record in traceback.format_exception(exc):
            for line in record.splitlines():
                print('  ' + line, file=sys.stderr)


def _warn(*args, **kwargs):
    warnings.warn(*args, **kwargs)


def _warn_future_us(message, remove):
    # Don't call warnings._deprecated() directly because we're lazily importing warnings and don't
    # want to have to trigger an eager import if it's not necessary.  Startup time matters a lot
    # here and warnings isn't cheap!  This inlines the check from
    # warnings._py_warnings._deprecated().
    _version = sys.version_info
    if (_version[:2] > remove) or (_version[:2] == remove and _version[3] != "alpha"):
        warnings._deprecated(message, remove=remove)


def makepath(*paths):
    dir = os.path.join(*paths)
    try:
        dir = os.path.abspath(dir)
    except OSError:
        pass
    return dir, os.path.normcase(dir)


def abs_paths():
    """Set __file__ to an absolute path."""
    for m in set(sys.modules.values()):
        loader_module = None
        try:
            loader_module = m.__loader__.__module__
        except AttributeError:
            try:
                loader_module = m.__spec__.loader.__module__
            except AttributeError:
                pass
        if loader_module not in {'_frozen_importlib', '_frozen_importlib_external'}:
            continue   # don't mess with a PEP 302-supplied __file__
        try:
            m.__file__ = os.path.abspath(m.__file__)
        except (AttributeError, OSError, TypeError):
            pass


def removeduppaths():
    """ Remove duplicate entries from sys.path along with making them
    absolute"""
    # This ensures that the initial path provided by the interpreter contains
    # only absolute pathnames, even if we're running from the build directory.
    L = []
    known_paths = set()
    for dir in sys.path:
        # Filter out duplicate paths (on case-insensitive file systems also
        # if they only differ in case); turn relative paths into absolute
        # paths.
        dir, dircase = makepath(dir)
        if dircase not in known_paths:
            L.append(dir)
            known_paths.add(dircase)
    sys.path[:] = L
    return known_paths


def _init_pathinfo():
    """Return a set containing all existing file system items from sys.path."""
    d = set()
    for item in sys.path:
        try:
            if os.path.exists(item):
                _, itemcase = makepath(item)
                d.add(itemcase)
        except TypeError:
            continue
    return d


# PEP 829 implementation notes.
#
# Startup information (.pth and .start file information) can be processed in
# implicit or explicit batches.  Implicit batches are handled by the site.py
# machinery automatically, while explicit batches are driven by user code and
# processed on boundaries defined by that code.
#
# addsitedir() calls which use the default defer_processing_start_files=False
# are self-contained: they create a per-call _StartupState, populate it from
# the site directory's .pth/.start files, run process() on it, and then throw
# the state away.  This is implicit batching and in that case the
# _startup_state global variable stays None.
#
# main() needs different semantics: it accumulates state across multiple
# addsitedir() calls (user-site plus all global site-packages) so that
# every sys.path extension is visible *before* any startup code (.pth
# import lines and .start entry points) runs.  Callers opt into this by
# passing defer_processing_start_files=True, which preserves the _StartupState
# into the global _startup_state.  Subsequent addsitedir() calls (with
# or without defer_processing_start_files=True) then write into that
# same shared state, and a later process_startup_files() call flushes
# all the state and resets the global to None.
#
# Here's the CRITICAL reentrancy invariant: process_startup_files() must clear
# the global _startup_state *before* calling state.process(), so that any
# reentrant site.addsitedir() calls reached from an exec'd .pth import line or
# a .start entry point falls into the per-call branch and gets its own fresh
# state.  Otherwise the recursive addsitedir() would mutate the very dicts
# that the outer state.process() is iterating.  This is the bug reported in
# gh-149504.
_startup_state = None


def _read_pthstart_file(sitedir, name, suffix):
    """Parse a .start or .pth file and return (lines, filename).

    On success, ``lines`` is a (possibly empty) list of the file's lines.
    On failure (file missing, hidden, unreadable, or .start with bad
    encoding), ``lines`` is ``None`` so callers can distinguish a
    successfully-read empty file from one that could not be read.
    """
    filename = os.path.join(sitedir, name)
    _trace(f"Reading startup configuration file: {filename}")

    try:
        st = os.lstat(filename)
    except OSError as exc:
        _trace(f"Cannot stat {filename!r}", exc)
        return None, filename

    if ((getattr(st, 'st_flags', 0) & stat.UF_HIDDEN) or
        (getattr(st, 'st_file_attributes', 0) & stat.FILE_ATTRIBUTE_HIDDEN)):
        _trace(f"Skipping hidden {suffix} file: {filename!r}")
        return None, filename

    _trace(f"Processing {suffix} file: {filename!r}")
    try:
        with io.open_code(filename) as f:
            raw_content = f.read()
    except OSError as exc:
        _trace(f"Cannot read {filename!r}", exc)
        return None, filename

    try:
        # Accept BOM markers in .start and .pth files as we do in source files
        # (Windows PowerShell 5.1 makes it hard to emit UTF-8 files without a BOM).
        content = raw_content.decode("utf-8-sig")
    except UnicodeDecodeError:
        _trace(f"Cannot read {filename!r} as UTF-8.")
        # For .pth files only, and then only until Python 3.20, fall back to
        # locale encoding for backward compatibility.
        _warn_future_us(
            ".pth files decoded to locale encoding as a fallback",
            remove=(3, 20)
        )
        if suffix == ".pth":
            content = raw_content.decode(locale.getencoding())
            _trace(f"Using fallback encoding {locale.getencoding()!r}")
        else:
            return None, filename

    return content.splitlines(), filename


class _StartupState:
    """Per-batch accumulator for .pth and .start file processing.

    A _StartupState collects sys.path extensions, deprecated .pth import
    lines, and .start entry points read from one or more site-packages
    directories.  Calling process() applies them in PEP 829 order: paths
    are added to sys.path first, then import lines from .pth files (skipping
    any with a matching .start), then entry points from .start files.

    State lives entirely on the instance; there is no module-level pending
    state.  This is what makes the module reentrancy-safe: a site.addsitedir()
    call reached recursively from an exec'd import line or a .start entry
    point operates on a different _StartupState than the one being processed
    by the outer call.

    The internal data is intentionally private; the public methods
    (read_pth_file, read_start_file, process) are the only supported write
    APIs.
    """
    __slots__ = ('_syspaths', '_importexecs', '_entrypoints')

    def __init__(self):
        # All three dicts map "<full path to .pth or .start file>" -> list
        # of items collected from that file.  Mapping by filename lets us
        # cross-reference a .pth and its matching .start (PEP 829 import
        # suppression rule) and lets _print_error report the source file
        # when an entry fails.
        self._syspaths = {}
        self._importexecs = {}
        self._entrypoints = {}

    def read_pth_file(self, sitedir, name, known_paths):
        """Parse a .pth file, accumulating sys.path extensions and import lines.

        Errors on individual lines do not abort processing of the rest of
        the file (PEP 829).  ``known_paths`` is the per-batch dedup
        ledger: any path already in it is skipped, and newly accepted
        paths are added to it so that subsequent .pth files in the same
        batch don't add them more than once.
        """
        lines, filename = _read_pthstart_file(sitedir, name, ".pth")
        if lines is None:
            return

        for n, line in enumerate(lines, 1):
            line = line.strip()
            if not line or line.startswith("#"):
                continue

            # In Python 3.18 and 3.19, `import` lines are silently
            # ignored.  In Python 3.20 and beyond, issue a warning when
            # `import` lines in .pth files are detected.
            if line.startswith(("import ", "import\t")):
                _warn_future_us(
                    "import lines in .pth files are silently ignored",
                    remove=(3, 18),
                )
                _warn_future_us(
                    "import lines in .pth files are noisily ignored",
                    remove=(3, 20),
                )
                self._importexecs.setdefault(filename, []).append(line)
                continue

            try:
                dir_, dircase = makepath(sitedir, line)
            except Exception as exc:
                _trace(f"Error in {filename!r}, line {n:d}: {line!r}", exc)
                continue

            # PEP 829 dedup: skip paths already seen in this batch.  See
            # _startup_state docstring above for batch lifetimes.
            if dircase in known_paths:
                _trace(
                    f"In {filename!r}, line {n:d}: "
                    f"skipping duplicate sys.path entry: {dir_}"
                )
            else:
                self._syspaths.setdefault(filename, []).append(dir_)
                known_paths.add(dircase)

    def read_start_file(self, sitedir, name):
        """Parse a .start file for a list of entry point strings."""
        lines, filename = _read_pthstart_file(sitedir, name, ".start")
        if lines is None:
            return

        # PEP 829: the *presence* of a matching .start file disables `import`
        # line processing in the matched .pth file, regardless of whether this
        # .start file contains any entry points.  Register the filename as a
        # key now so an empty (or comment-only) .start file still suppresses.
        entrypoints = self._entrypoints.setdefault(filename, [])

        for n, line in enumerate(lines, 1):
            line = line.strip()
            if not line or line.startswith("#"):
                continue
            # Syntax validation is deferred to entry point execution
            # time, where pkgutil.resolve_name(strict=True) enforces the
            # pkg.mod:callable form.
            entrypoints.append(line)

    def process(self):
        """Apply accumulated state in PEP 829 order.

        Phase order matters: all .pth path extensions are applied to
        sys.path *before* any import line or .start entry point runs, so
        that an entry point may live in a module reachable only via a
        .pth-extended path.
        """
        self._extend_syspath()
        self._exec_imports()
        self._execute_start_entrypoints()

    def _extend_syspath(self):
        # Duplicates have already been filtered (in existing sys.path or
        # across .pth files via known_paths), and entries are already
        # abspath/normpath'd, so all that remains is to confirm the path
        # exists.
        for filename, dirs in self._syspaths.items():
            for dir_ in dirs:
                if os.path.exists(dir_):
                    _trace(f"Extending sys.path with {dir_} from {filename}")
                    sys.path.append(dir_)
                else:
                    _print_error(
                        f"In {filename}: {dir_} does not exist; "
                        f"skipping sys.path append"
                    )

    def _exec_imports(self):
        # For each `import` line we've seen in a .pth file, exec() it in
        # order, unless the .pth has a matching .start file in this same
        # batch.  In that case, PEP 829 says the import lines are
        # suppressed in favor of the .start's entry points.
        for filename, imports in self._importexecs.items():
            # Given "/path/to/foo.pth", check whether "/path/to/foo.start" was
            # registered in this same batch.
            name, dot, pth = filename.rpartition(".")
            assert dot == "." and pth == "pth", (
                f"Bad startup filename: {filename}"
            )
            if f"{name}.start" in self._entrypoints:
                _trace(
                    f"import lines in {filename} are suppressed "
                    f"due to matching {name}.start file."
                )
                continue

            _trace(
                f"import lines in {filename} are deprecated, "
                f"use entry points in a {name}.start file instead."
            )
            for line in imports:
                try:
                    _trace(f"Exec'ing from {filename}: {line}")
                    exec(line)
                except Exception as exc:
                    _print_error(
                        f"Error in import line from {filename}: {line}",
                        exc,
                    )

    def _execute_start_entrypoints(self):
        # Resolve each entry point string to a callable via
        # pkgutil.resolve_name(strict=True), which both validates the
        # required pkg.mod:callable form and performs the import in one
        # step, then call it with no arguments.
        for filename, entrypoints in self._entrypoints.items():
            for entrypoint in entrypoints:
                try:
                    _trace(
                        f"Executing entry point: {entrypoint} from {filename}"
                    )
                    callable_ = pkgutil.resolve_name(entrypoint, strict=True)
                except ValueError as exc:
                    _print_error(
                        f"Invalid entry point syntax in {filename}: "
                        f"{entrypoint!r}",
                        exc,
                    )
                except Exception as exc:
                    _print_error(
                        f"Error resolving entry point {entrypoint} "
                        f"from {filename}",
                        exc,
                    )
                else:
                    try:
                        callable_()
                    except Exception as exc:
                        _print_error(
                            f"Error in entry point {entrypoint} from {filename}",
                            exc,
                        )


def process_startup_files():
    """Flush any pending startup-file state accumulated during a batch.

    Used by main() (and any external caller that drove addsitedir() with
    defer_processing_start_files=True) to apply the accumulated paths
    and run the deferred import lines / entry points.

    Reentrancy: the active batch state is detached from _startup_state
    *before* state.process() runs.  This way, if an exec'd import line
    or .start entry point itself calls site.addsitedir(), that call
    creates its own per-call _StartupState rather than mutating the dicts
    being iterated here.  See gh-149504.
    """
    global _startup_state
    if _startup_state is None:
        return
    state, _startup_state = _startup_state, None
    state.process()


def addpackage(sitedir, name, known_paths):
    """Process a .pth file within the site-packages directory."""
    if known_paths is None:
        known_paths = _init_pathinfo()
        reset = True
    else:
        reset = False

    # If a batch is already in progress (for example, main() is still
    # accumulating sitedirs), participate in the batch by writing into the
    # shared _startup_state and letting the eventual process_startup_files()
    # flush it. Otherwise this is a standalone call, so create a unique
    # per-call state, populate it, and process it before returning.
    if _startup_state is None:
        state = _StartupState()
        state.read_pth_file(sitedir, name, known_paths)
        state.process()
    else:
        _startup_state.read_pth_file(sitedir, name, known_paths)

    return None if reset else known_paths


def addsitedir(sitedir, known_paths=None, *, defer_processing_start_files=False):
    """Add 'sitedir' argument to sys.path if missing and handle startup
    files."""
    global _startup_state
    _trace(f"Adding directory: {sitedir!r}")
    if known_paths is None:
        known_paths = _init_pathinfo()
        reset = True
    else:
        reset = False
    sitedir, sitedircase = makepath(sitedir)

    # If the normcase'd new sitedir isn't already known, append it to
    # sys.path, keep a record of it, and process all .pth and .start files
    # found in that directory.  If the new sitedir is known, be sure not
    # to process all of those more than once!  gh-75723
    if sitedircase not in known_paths:
        sys.path.append(sitedir)
        known_paths.add(sitedircase)

        try:
            names = os.listdir(sitedir)
        except OSError:
            return None if reset else known_paths

        # Pick the _StartupState we'll write into.  There are three cases:
        #
        # 1. A batch is already active (_startup_state is set, e.g.  because
        #    main() previously called us with
        #    defer_processing_start_files=True).  Participate in this batch by
        #    sharing the same state.  Don't flush the state since the batch's
        #    eventual process_startup_files() will do that.
        #
        # 2. There is no active batch but the caller passed
        #    defer_processing_start_files=True.  Preserve a fresh
        #    _StartupState into the global _startup_state so that subsequent
        #    addsitedir() calls participate in this batch, and so that the
        #    caller's later process_startup_files() finds it.
        #
        # 3. This is a standalone call (there is no active batch and
        #    defer_processing_start_files=False).  Create a unique per-call
        #    state, populate it, process it, and then clear it.  Per-call
        #    state is what makes reentrant addsitedir() safe; a recursive call
        #    from inside process() lands here too and gets its own independent
        #    state.

        if _startup_state is not None:
            state = _startup_state
            flush_now = False
        elif defer_processing_start_files:
            state = _startup_state = _StartupState()
            flush_now = False
        else:
            state = _StartupState()
            flush_now = True

        # The following phases are defined by PEP 829.
        # Phases 1-3: Read .pth files, accumulating paths and import lines.
        pth_names = sorted(
            name for name in names
            if name.endswith(".pth") and not name.startswith(".")
        )
        for name in pth_names:
            state.read_pth_file(sitedir, name, known_paths)

        # Phases 6-7: Discover .start files and accumulate their entry points.
        # Import lines from .pth files with a matching .start file are
        # discarded at flush time by _StartupState._exec_imports().
        start_names = sorted(
            name for name in names
            if name.endswith(".start") and not name.startswith(".")
        )
        for name in start_names:
            state.read_start_file(sitedir, name)

        if flush_now:
            state.process()

    return None if reset else known_paths


def check_enableusersite():
    """Check if user site directory is safe for inclusion

    The function tests for the command line flag (including environment var),
    process uid/gid equal to effective uid/gid.

    None: Disabled for security reasons
    False: Disabled by user (command line option)
    True: Safe and enabled
    """
    if sys.flags.no_user_site:
        return False

    if hasattr(os, "getuid") and hasattr(os, "geteuid"):
        # check process uid == effective uid
        if os.geteuid() != os.getuid():
            return None
    if hasattr(os, "getgid") and hasattr(os, "getegid"):
        # check process gid == effective gid
        if os.getegid() != os.getgid():
            return None

    return True


# NOTE: sysconfig and it's dependencies are relatively large but site module
# needs very limited part of them.
# To speedup startup time, we have copy of them.
#
# See https://bugs.python.org/issue29585

# Copy of sysconfig._get_implementation()
def _get_implementation():
    return 'Python'

# Copy of sysconfig._getuserbase()
def _getuserbase():
    env_base = os.environ.get("PYTHONUSERBASE", None)
    if env_base:
        return env_base

    # Emscripten, iOS, tvOS, VxWorks, WASI, and watchOS have no home directories
    if sys.platform in {"emscripten", "ios", "tvos", "vxworks", "wasi", "watchos"}:
        return None

    def joinuser(*args):
        return os.path.expanduser(os.path.join(*args))

    if os.name == "nt":
        base = os.environ.get("APPDATA") or "~"
        return joinuser(base, _get_implementation())

    if sys.platform == "darwin" and sys._framework:
        return joinuser("~", "Library", sys._framework,
                        "%d.%d" % sys.version_info[:2])

    return joinuser("~", ".local")


# Same to sysconfig.get_path('purelib', os.name+'_user')
def _get_path(userbase):
    version = sys.version_info
    if hasattr(sys, 'abiflags') and 't' in sys.abiflags:
        abi_thread = 't'
    else:
        abi_thread = ''

    implementation = _get_implementation()
    implementation_lower = implementation.lower()
    if os.name == 'nt':
        ver_nodot = sys.winver.replace('.', '')
        return f'{userbase}\\{implementation}{ver_nodot}\\site-packages'

    if sys.platform == 'darwin' and sys._framework:
        return f'{userbase}/lib/{implementation_lower}/site-packages'

    return f'{userbase}/lib/{implementation_lower}{version[0]}.{version[1]}{abi_thread}/site-packages'


def getuserbase():
    """Returns the `user base` directory path.

    The `user base` directory can be used to store data. If the global
    variable ``USER_BASE`` is not initialized yet, this function will also set
    it.
    """
    global USER_BASE
    if USER_BASE is None:
        USER_BASE = _getuserbase()
    return USER_BASE


def getusersitepackages():
    """Returns the user-specific site-packages directory path.

    If the global variable ``USER_SITE`` is not initialized yet, this
    function will also set it.
    """
    global USER_SITE, ENABLE_USER_SITE
    userbase = getuserbase() # this will also set USER_BASE

    if USER_SITE is None:
        if userbase is None:
            ENABLE_USER_SITE = False # disable user site and return None
        else:
            USER_SITE = _get_path(userbase)

    return USER_SITE

def addusersitepackages(known_paths, *, defer_processing_start_files=False):
    """Add a per user site-package to sys.path

    Each user has its own python directory with site-packages in the
    home directory.
    """
    # get the per user site-package path
    # this call will also make sure USER_BASE and USER_SITE are set
    _trace("Processing user site-packages")
    user_site = getusersitepackages()

    if ENABLE_USER_SITE and os.path.isdir(user_site):
        addsitedir(user_site, known_paths, defer_processing_start_files=defer_processing_start_files)
    return known_paths

def getsitepackages(prefixes=None):
    """Returns a list containing all global site-packages directories.

    For each directory present in ``prefixes`` (or the global ``PREFIXES``),
    this function will find its `site-packages` subdirectory depending on the
    system environment, and will return a list of full paths.
    """
    sitepackages = []
    seen = set()

    if prefixes is None:
        prefixes = PREFIXES

    for prefix in prefixes:
        if not prefix or prefix in seen:
            continue
        seen.add(prefix)

        implementation = _get_implementation().lower()
        ver = sys.version_info
        if hasattr(sys, 'abiflags') and 't' in sys.abiflags:
            abi_thread = 't'
        else:
            abi_thread = ''
        if os.sep == '/':
            libdirs = [sys.platlibdir]
            if sys.platlibdir != "lib":
                libdirs.append("lib")

            for libdir in libdirs:
                path = os.path.join(prefix, libdir,
                                    f"{implementation}{ver[0]}.{ver[1]}{abi_thread}",
                                    "site-packages")
                sitepackages.append(path)
        else:
            sitepackages.append(prefix)
            sitepackages.append(os.path.join(prefix, "Lib", "site-packages"))
    return sitepackages

def addsitepackages(known_paths, prefixes=None, *, defer_processing_start_files=False):
    """Add site-packages to sys.path"""
    _trace("Processing global site-packages")
    for sitedir in getsitepackages(prefixes):
        if os.path.isdir(sitedir):
            addsitedir(sitedir, known_paths, defer_processing_start_files=defer_processing_start_files)

    return known_paths

def setquit():
    """Define new builtins 'quit' and 'exit'.

    These are objects which make the interpreter exit when called.
    The repr of each object contains a hint at how it works.

    """
    if os.sep == '\\':
        eof = 'Ctrl-Z plus Return'
    else:
        eof = 'Ctrl-D (i.e. EOF)'

    builtins.quit = _sitebuiltins.Quitter('quit', eof)
    builtins.exit = _sitebuiltins.Quitter('exit', eof)


def setcopyright():
    """Set 'copyright' and 'credits' in builtins"""
    builtins.copyright = _sitebuiltins._Printer("copyright", sys.copyright)
    builtins.credits = _sitebuiltins._Printer("credits", """\
Thanks to CWI, CNRI, BeOpen, Zope Corporation, the Python Software
Foundation, and a cast of thousands for supporting Python
development.  See www.python.org for more information.""")
    files, dirs = [], []
    # Not all modules are required to have a __file__ attribute.  See
    # PEP 420 for more details.
    here = getattr(sys, '_stdlib_dir', None)
    if not here and hasattr(os, '__file__'):
        here = os.path.dirname(os.__file__)
    if here:
        files.extend(["LICENSE.txt", "LICENSE"])
        dirs.extend([os.path.join(here, os.pardir), here, os.curdir])
    builtins.license = _sitebuiltins._Printer(
        "license",
        "See https://www.python.org/psf/license/",
        files, dirs)


def sethelper():
    builtins.help = _sitebuiltins._Helper()


def gethistoryfile():
    """Check if the PYTHON_HISTORY environment variable is set and define
    it as the .python_history file.  If PYTHON_HISTORY is not set, use the
    default .python_history file.
    """
    if not sys.flags.ignore_environment:
        history = os.environ.get("PYTHON_HISTORY")
        if history:
            return history
    return os.path.join(os.path.expanduser('~'),
        '.python_history')


def enablerlcompleter():
    """Enable default readline configuration on interactive prompts, by
    registering a sys.__interactivehook__.
    """
    sys.__interactivehook__ = register_readline


def register_readline():
    """Configure readline completion on interactive prompts.

    If the readline module can be imported, the hook will set the Tab key
    as completion key and register ~/.python_history as history file.
    This can be overridden in the sitecustomize or usercustomize module,
    or in a PYTHONSTARTUP file.
    """
    if not sys.flags.ignore_environment:
        PYTHON_BASIC_REPL = os.getenv("PYTHON_BASIC_REPL")
    else:
        PYTHON_BASIC_REPL = False

    import atexit

    try:
        try:
            import readline
        except ImportError:
            readline = None
        else:
            import rlcompleter  # noqa: F401
    except ImportError:
        return

    try:
        if PYTHON_BASIC_REPL:
            CAN_USE_PYREPL = False
        else:
            original_path = sys.path
            sys.path = [p for p in original_path if p != '']
            try:
                import _pyrepl.readline
                if os.name == "nt":
                    import _pyrepl.windows_console
                    console_errors = (_pyrepl.windows_console._error,)
                else:
                    import _pyrepl.unix_console
                    console_errors = _pyrepl.unix_console._error
                from _pyrepl.main import CAN_USE_PYREPL
            except ModuleNotFoundError:
                CAN_USE_PYREPL = False
            finally:
                sys.path = original_path
    except ImportError:
        return

    if readline is not None:
        # Reading the initialization (config) file may not be enough to set a
        # completion key, so we set one first and then read the file.
        if readline.backend == 'editline':
            readline.parse_and_bind('bind ^I rl_complete')
        else:
            readline.parse_and_bind('tab: complete')

        try:
            readline.read_init_file()
        except OSError:
            # An OSError here could have many causes, but the most likely one
            # is that there's no .inputrc file (or .editrc file in the case of
            # Mac OS X + libedit) in the expected location.  In that case, we
            # want to ignore the exception.
            pass

    if readline is None or readline.get_current_history_length() == 0:
        # If no history was loaded, default to .python_history,
        # or PYTHON_HISTORY.
        # The guard is necessary to avoid doubling history size at
        # each interpreter exit when readline was already configured
        # through a PYTHONSTARTUP hook, see:
        # http://bugs.python.org/issue5845#msg198636
        history = gethistoryfile()

        if CAN_USE_PYREPL:
            readline_module = _pyrepl.readline
            exceptions = (OSError, *console_errors)
        else:
            if readline is None:
                return
            readline_module = readline
            exceptions = OSError

        try:
            readline_module.read_history_file(history)
        except exceptions:
            pass

        def write_history():
            try:
                readline_module.write_history_file(history)
            except FileNotFoundError, PermissionError:
                # home directory does not exist or is not writable
                # https://bugs.python.org/issue19891
                pass
            except OSError:
                if errno.EROFS:
                    pass  # gh-128066: read-only file system
                else:
                    raise

        atexit.register(write_history)


def venv(known_paths):
    global PREFIXES, ENABLE_USER_SITE

    env = os.environ
    if sys.platform == 'darwin' and '__PYVENV_LAUNCHER__' in env:
        executable = sys._base_executable = os.environ['__PYVENV_LAUNCHER__']
    else:
        executable = sys.executable
    exe_dir = os.path.dirname(os.path.abspath(executable))
    site_prefix = os.path.dirname(exe_dir)
    sys._home = None
    conf_basename = 'pyvenv.cfg'
    candidate_conf = next(
        (
            conffile for conffile in (
                os.path.join(exe_dir, conf_basename),
                os.path.join(site_prefix, conf_basename)
            )
            if os.path.isfile(conffile)
        ),
        None
    )

    if candidate_conf:
        virtual_conf = candidate_conf
        system_site = "true"
        # Issue 25185: Use UTF-8, as that's what the venv module uses when
        # writing the file.
        with open(virtual_conf, encoding='utf-8') as f:
            for line in f:
                if '=' in line:
                    key, _, value = line.partition('=')
                    key = key.strip().lower()
                    value = value.strip()
                    if key == 'include-system-site-packages':
                        system_site = value.lower()
                    elif key == 'home':
                        sys._home = value

        if sys.prefix != site_prefix:
            _warn(f'Unexpected value in sys.prefix, expected {site_prefix}, got {sys.prefix}', RuntimeWarning)
        if sys.exec_prefix != site_prefix:
            _warn(f'Unexpected value in sys.exec_prefix, expected {site_prefix}, got {sys.exec_prefix}', RuntimeWarning)

        # Doing this here ensures venv takes precedence over user-site
        addsitepackages(known_paths, [sys.prefix])

        if system_site == "true":
            PREFIXES += [sys.base_prefix, sys.base_exec_prefix]
        else:
            ENABLE_USER_SITE = False

    return known_paths


def execsitecustomize():
    """Run custom site specific code, if available."""
    try:
        try:
            import sitecustomize  # noqa: F401
        except ImportError as exc:
            if exc.name == 'sitecustomize':
                pass
            else:
                raise
    except Exception as err:
        if sys.flags.verbose:
            sys.excepthook(*sys.exc_info())
        else:
            sys.stderr.write(
                "Error in sitecustomize; set PYTHONVERBOSE for traceback:\n"
                "%s: %s\n" %
                (err.__class__.__name__, err))


def execusercustomize():
    """Run custom user specific code, if available."""
    try:
        try:
            import usercustomize  # noqa: F401
        except ImportError as exc:
            if exc.name == 'usercustomize':
                pass
            else:
                raise
    except Exception as err:
        if sys.flags.verbose:
            sys.excepthook(*sys.exc_info())
        else:
            sys.stderr.write(
                "Error in usercustomize; set PYTHONVERBOSE for traceback:\n"
                "%s: %s\n" %
                (err.__class__.__name__, err))


def main():
    """Add standard site-specific directories to the module search path.

    This function is called automatically when this module is imported,
    unless the python interpreter was started with the -S flag.
    """
    global ENABLE_USER_SITE

    orig_path = sys.path[:]
    known_paths = removeduppaths()
    if orig_path != sys.path:
        # removeduppaths() might make sys.path absolute.
        # Fix __file__ of already imported modules too.
        abs_paths()

    known_paths = venv(known_paths)
    if ENABLE_USER_SITE is None:
        ENABLE_USER_SITE = check_enableusersite()
    known_paths = addusersitepackages(known_paths, defer_processing_start_files=True)
    known_paths = addsitepackages(known_paths, defer_processing_start_files=True)
    # PEP 829: flush accumulated data from all .pth and .start files.
    # Paths are extended first, then deprecated import lines are exec'd,
    # and finally .start entry points are executed — ensuring sys.path is
    # fully populated before any startup code runs.  process_startup_files()
    # also clears the pending state so a later addsitedir() call does
    # not re-apply already-processed data.
    process_startup_files()
    setquit()
    setcopyright()
    sethelper()
    if not sys.flags.isolated:
        enablerlcompleter()
    execsitecustomize()
    if ENABLE_USER_SITE:
        execusercustomize()

# Prevent extending of sys.path when python was started with -S and
# site is imported later.
if not sys.flags.no_site:
    main()

def _script():
    help = """\
    %s [--user-base] [--user-site]

    Without arguments print some useful information
    With arguments print the value of USER_BASE and/or USER_SITE separated
    by '%s'.

    Exit codes with --user-base or --user-site:
      0 - user site directory is enabled
      1 - user site directory is disabled by user
      2 - user site directory is disabled by super user
          or for security reasons
     >2 - unknown error
    """
    args = sys.argv[1:]
    if not args:
        user_base = getuserbase()
        user_site = getusersitepackages()
        print("sys.path = [")
        for dir in sys.path:
            print("    %r," % (dir,))
        print("]")
        def exists(path):
            if path is not None and os.path.isdir(path):
                return "exists"
            else:
                return "doesn't exist"
        print(f"USER_BASE: {user_base!r} ({exists(user_base)})")
        print(f"USER_SITE: {user_site!r} ({exists(user_site)})")
        print(f"ENABLE_USER_SITE: {ENABLE_USER_SITE!r}")
        sys.exit(0)

    buffer = []
    if '--user-base' in args:
        buffer.append(USER_BASE)
    if '--user-site' in args:
        buffer.append(USER_SITE)

    if buffer:
        print(os.pathsep.join(buffer))
        if ENABLE_USER_SITE:
            sys.exit(0)
        elif ENABLE_USER_SITE is False:
            sys.exit(1)
        elif ENABLE_USER_SITE is None:
            sys.exit(2)
        else:
            sys.exit(3)
    else:
        import textwrap
        print(textwrap.dedent(help % (sys.argv[0], os.pathsep)))
        sys.exit(10)

if __name__ == '__main__':
    _script()